Television receiver



Sept. 27, 1960 J. G. SPRACKLEN TELEVISION RECEIVER 3 Sheets-Sheet 1Original Filed Nov. 17. 1952 HIS ATTORNEY Sept. 27, 1960 J. G. SPRACKLEN2,954,430

TELEVISION RECEIVER Original Filed Nov. 17, 1952 3 Sheets-Sheet 2 FIG.2

FlG.4

FIG. 3

IOI

FIG.5

JOHN G. SPRACKLEN IN V EN TOR.

0 ina- 934 HIS ATTORNEY.

S p 7, 1960 J. G. SPRACKLEN TELEVISION'RECEIVER 3 Sheets-Sheet 3Original Filed Nov. 17. 1952 JOHN G. SPRACKLE N INVENTOR. BY g HATTORNEY...

TELEVISION RECEIVER John G. Sprackl en, Chicago, ]]l., assignor toZenith Radio Corporation, a corporation of Delaware 9'Clairns. c1.178-7.5)

This application is a division of a previously filed copendingapplication Serial No. 320,866, filed Novemnited States Patent ber 17,1952, now Patent No. 2,875,331, issued Feb.

24, 1959, and assigned to the present assignee. This invention relatesgenerally to television receivers and more particularly to synchronizingand automatic gain control systems for use in such receivers.

In United States PatentNo. 2,606,300, issued August 5, 1952, forElectron-Discharge Device and in the copending application of RobertAdler, Serial No. 267,826, filed January 23, 1952, now Patent No.2,684,404, issued July 20, 1954, for Frequency Controllable OscillatingSystems, both assigned to the present assignee, there are disclosed andclaimed a novel electron-discharge device :and system for use as asynchronizing-control arrangement in a television receiver or the like.In the preferred embodiment, a two-section tube is em ployed, the firstor control section operating as a synchronizing-signal clipper andbalanced line-frequency phase-detector to develop between a pair ofanodes a balanced unidirectional control voltage indicative of the phasedifference between the local line-frequency oscillator and the incomingline-frequency synchronizingsignal pulses. In the second or powersection of the tube, w

an electron beam is simultaneously subjected to a sinusoidalmagnetic-deflection field energized from the linefrequency sweep outputand to a slow lateral displacement in accordance with the balancedunidirectional control voltage developed between the two phase-detectoranodes in the first section. In this manner, the duty cycles of the twofinal anodes in the secondsection of the tube are caused to vary inaccordance with the unidirectional control potential developed betweenthe phase-detector anodes of the first section. Either the leading edgeor the trailing edge of the developed quasi-square wave is employed todrive the line-frequency sweep system. The output voltages appearing atthe phase-detector anodes may be combined and integrated to providefield-freg5, quency output pulses for controlling the field-frequencysweep system, or a separate anode may be provided for this purpose.Thus, a single tube, together with a small number of external circuitelements, performs the several functions of synchronizing-signalseparator, automatic-frequency-control (AFC) phase-detector,line-frequency oscillator, and reactance tube, providing a substantialsaving in comparison with conventional systems which usually employthree or more tubes to perform these functions.

In the copending applications of Robert Adler, Serial a No. 242,509,filed August 18, 1951, now Patent No. 2,717,972, issued September 13,1955, entitled Electron- Discharge Device, and Serial No. 314,373, filedOctober 11, 1952, entitled Television Receiver, and both assigned to thepresent assignee, there are disclosed and claimed a novel tube andsystem for obtaining both noiseimmune synchronizing-signal separationand automatic gain control generation. In a preferred form of thissystem, a sheet-like electron beam of substantially rec- Patented Sept.27, 19160 ice . 2. tangular cross-section is projected through adeflectioncontrol system toward a target electrode which is providedwith a pair of apertures and is followed by plate electrodes forcollecting space electrons which pass through the respective apertures.Detected composite video signals are applied. to the deflection-controlsystem in such a manner that space. electrons are permitted to passthrough the two apertures in the target electrode only duringsynchronizing-pulse intervals. Moreover, extraneous noise impulses,which are generally of much greater amplitude than theldesiredsynchronizing pulses, cause transverse deflection of thebeam beyond. theaper: tures so that space electron flow to the plate electrodes is againinterrupted. One of the plate electrodes is employed to derivenoise-immune output current pulses corresponding to thesynchronizing-pulse components of the applied composite video signals,and these output pulses drive the line-frequency and field-frequencyscanning systems. The other plate electrode is utilized to develop anautom-atic-gain-control (AGC) potential which is then applied in aconventional manner to one or more of the early receiving stages. Inorder to insure the establishment of synchronizing-pulse output at thefirst plate electrode whenever the automatic gain, control system goesinto effect to limit further growth of the signal, the two apertures inthe target electrode are disposed in overlapping alignment in adirection parallel to the plane of the sheet-like electron beam. Inaddition to providing noise-immune synchronizing-signal separation andautomatic gain control generation in a single tube, this system has theimportantadvantage of automatically establishing the correctsynchronizing-signal clipping level for all normal receiver-input signallevels, with the result that incorrect synchronizing-pulse clippingwhich might otherwise be caused by drift or misadjustment of theautomatic gain control circuits is effectively precluded. Further noiseimmunity may be provided, if desired, by applying a gating signal to theAGC output plate, although it is preferred toemploy continuousenergization of the AGC plate in the manner disclosed and claimed in thecopending application of John G. Spracklen, Serial No. 281,708, filedApril 12, 1952, now abandoned, for TelevisionReceiver and also assignedto the present assignee, since adequate noise immunity is obtained inthis manner without the added complexity introduced by time gating.

In the copending application of John G. Spracklen, Serial No. 246,768,filed September 15, 1951, now Patent No. 2,768,319, issued October 23,1956, for Electron- Discharge Device, and assigned to" the presentassignee, there are disclosed and claimed a still further noveltube andsystem for combining certain features embodied in the systems of theaforementioned Adler applications.- To achieve this objective, therequirement for a magnetic deflection field is obviated by modifying thetube construction and external circuit connections to provide phasedetection by means ofa gating action. To this end, the singlesynchronizing-signal output plate of the last-mentioned Adler tube isreplaced by at least a pair of phase-detector plate electrodessymmetrically positionedbehind the sync clipping aperture. A balancedcomparison signal is applied between; the two phase detector plates fromthe line-frequency scanning system of the receiver. Whenthe desiredcondition of phase synchronism exists, the phase-detector plates aremaintained at equal average potentials; however, upon deviation fromsynchronism; a balanced control potential indicative ofthe magnitude anddirection of the deviation is developed. In accordance with a preferredembodiment, this system is employed in conjunction with adeflection-tube oscillator, and the phase-detector plate electrodes aredirect-coupled to the deflection electrodes of the oscillator to efieetautomatic frequency control.

While the tubes and systems described and claimed in the aforementionedcopending applications are operative and afford numerous advantages overconventional synchronizing and automatic gain control systems, it hasbeen found that certain difficulties of a practical nature may beencountered. When continuous energization of the AGC plate is employedin the manner described in application Serial No. 281,708, it isnecessary to provide a source of unidirectional negative bias potentialin order to translate the AGC potential to an average level suitable forapplication to the control grids of the RF and IF amplifier stages andto provide a suitable amplitude delay characteristic. The use of abattery to provide this negative bias voltage is undesirable because ofthe necessity of replacement at periodic intervals. It is possible toemploy a diode rectifier for this purpose, although this solution isuneconomical and requires an additional tube.

Moreover, it has been found that the deflectors in the power section ofthe tube may draw beam current during the portions of each operatingcycle when the beam is subjected to its maximum lateral deflection ineach direction; since these deflectors are direct-coupled to thephase-detector anodes in the control section of the tube, the averagephase-detector anode voltage may fall, leading to instability orcollapse of the automatic frequency control action.

It is therefore an important object of the present invention to providea new and improved synchronizing system for use in a televisionreceiver, of the type disclosed and claimed in the above-identifiedAdler and/or Spracklen applications.

It is a more-specific object of the invention to provide such a new andimproved system in which the require ment of a battery or an extra diodefor providing a negative bias voltage for the automatic gain controlsystem is obviated.

Yet another object of the invention is to avoid instability or collapseof the automatic frequency control system attributable to current flowto the deflectors in the power section of the tube. 7

Still another object of the invention is to effect a current saving inthe power section of the tube by reducing the duty cycle of the outputelectrode system.

In accordance wtih the present invention, these and other objects areaccomplished by applying a gating signal to an intensity-controlelectrode, preferably a focusing electrode, in the power section of thetube to prevent the fiow of space current to the output electrode systemexcept during a minor portion of each scanning cycle, thus reducing themaximum lateral swing of the electron beam and reducing the duty cycleof the output electrode system. As an additional feature of theinvention, the same intensity-control electrode serves as a diode platefor developing a unidirectional negative bias voltage for application tothe automatic gain control sysi tern, thus eliminating the necessity forproviding a battery or an additional diode.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The invention,together with further objects and advantages thereof, may best beunderstood, however, by reference to the following description taken inconnection with the accompanying drawings, in the several figures ofwhich like reference numerals indicate like elements, and in which:

.Figure 1 is a schematic diagram of a television receiver embodying thepresent invention;

Figure 2 is a cross-sectional view of the electrode system of anelectron-discharge device employed in the receiver of Figure 1;

Figure 3 is a cross-sectional view taken along the line 33 of Figure 2,and

Figures 4-6 are graphical representations useful in understanding theoperation of the present invention.

Throughout the specification and the appended claims, the term compositetelevision signal is employed to describe the received modulated carriersignal, while the term composite video signal is employed to denote thevarying unidirectional or unipolar signal after detection. The termdirect-coupling is descriptive of a circuit coupling capable oftransmitting direct or unidirectional voltages, and a direct connectionis a direct-coupling of substantially zero impedance.

,In the television receiver of Figure 1, incoming composite televisionsignals are received by an antenna '10 and impressed on aradio-frequency amplifier 11. The amplified composite television signalsfrom radio-frequency amplifier 11 are supplied to anoscillator-converter 12, and the intermediate-frequency output signalsfrom oscillator-converter 12 are impressed on an intermediate-frequencyamplifier 13. The amplified intermediate-frequency composite televisionsignals are demodulated by a video detector 14, and the video-signalcomponents of the resulting composite video signals are impressed on theinput circuit of an image-reproducing device 15, such as a cathode-raytube, after amplification by first and second video amplifiers 16 and17. 'Intercarrier sound signals developed in the output circuit of firstvideo amplifier 16 are applied to suitable sound circuits 18, which maycomprise a limiter-discriminator and audio and power amplifier stages,and the amplified audio signals are impressed on a loudspeaker 19 orother soundreproducing device.

Composite video signals from first video amplifier 16 are supplied to asynchronizing and automatic gain control system 20 embodying the presentinvention, and suitable line-frequency and field-frequency scanningsignals are impressed on appropriate line-frequency and field-frequencydeflection coils 21 and 22 associated with image-reproducing device 15.

The basic construction and operation of synchronizing and automatic gaincontrol system 20 are specifically described in the Spracklenapplication Serial No. 246,768. This system is built around a specialpurpose electron tube 23 of novel construction which combines theseveral functions of noise-immune synchronizing-signal separation,automatic-frequency-control phase-detection, generation ofline-frequency oscillations, frequency control of the line-frequencyoscillations, and automatic gain control generation. To facilitate thefollowing description of the construction and operation of the receiverof Figure 1, reference is now made to Figures 2-5.

In Figure 2, which is a cross-sectional view of special purpose electrontube 23, two separate sheet-like eiectron beams of substantiallyrectangular cross-section are projected from opposite electron-emissivesurfaces of a common elongated cathode 25 which is provided with anindirect heater element 26. In the right-hand or control section of thetube, space electrons originating at cathode 25 are projected through aslot 27 in an accelerating electrode 23 toward a target electrode orintercepting anode 29 which is provided with a pair of rectangularapertures or slots 39 and 31, best visualized from the view of Figure 3.Preferably, slots 3i; and 31 are arranged in overlapping alignment in adirection parallel to cathode 25, and slot 31 may be provided with alateral extension 32 for a purpose to be hereinafter described. A pairof receptor electrodes 33 and 34 constituting a first output electrodesystem, are provided for collectively receiving space electrons whichpass through slot 3%, and an additional plate electrode 35, constitutinga second output electrode system, is provided for receiving spaceelectrons which pass through slot 31. Receptor electrodes .33 and 34 arepreferably constructed as controllector electrodes each having adeflection-control portion and a collector portion and adapted to bebiased at equal positive operating voltages in the manner described andclaimed in the copending application of Robert Adler, Serial No.263,737, filedDecember 28, 1951, now Patent No." 2,741,721, issued April10, 1956, for Electron- Discharge Device, and assigned to the presentassignee. However, output electrodes 33 and 34 may be formed in anyother desired manner, for example as a pair of simple transversecollecting plates such as those described in the Spracklen applicationSerial No. 246,768, without departing from the spirit of the presentinvention.

A deflection-control system, illustrated as a pair ofelectrostatic-deflection electrodes or plates 36 and 37, is providedbetween accelerating electrode 28 and target electrode 29. Deflectors 36and 37 extend for the full height of the beam to constitute a singleinput electrode system associated with both out-put electrode systems.At least the active deflector 37 is preferably of louvred constructionas shown in Figure 2 and described and claimed in the copendingapplication of Robert Adler, Serial No. 277,399, filed March 19, 1952,now Patent No. 2,691,117, issued October 5, 1954, for Electron-Discharge Device and assigned to the present assignee, in order tominimize the amount of beam current drawn by the active deflector understrong impulse noiseconditions. The passive or companion deflector 36may also advantageously be constructed in the same manner (not shown) toavoid deleterious effects of secondary electron emission resulting fromimpingement of space electrons under certain operating conditions.Preferably the tube is so constructed and operated that the thickness ofthe beam at the plane of target electrode 29 is less than the width ofslot 30.

In the left-hand or power section of the tube, electrons originating atcathode 25 are projected through slotted focusing and acceleratingelectrodes 38 and 39 toward an output system comprising a pair of anodes40 and 41 respectively having active portions on opposite sides of thetube axis or undeflected path 42 of this second beam. A pair ofelectrostatic-deflection electrodes 43 and 44 are provided between slot38 and anodes 40 and 41. A focusing electrode 46, having a slot narrowerthan the emissive surface of cathode 25, may be interposed betweencathode 25 and accelerating electrode 28 and maintained at or nearcathode potential to restrict electron emission in the control sectionof the tube to a narrow central portion of the emissive surface.

Those elements thus far described constitute the essential elements of aspecial purpose electron tube suitable for use in the synchronizing andAGC system 26 of the receiver of Figure 1. However, refinements of thiselectrode system may be made in accordance with well known practices inthe art. Thus, it may be advantageous to include one or more suppressorelectrodes, such as electrode 48, between intercepting anode 29 andelectrodes 33, 34 and 35, and to form target electrode 29 with flanges49 and 50 directed toward the electron gun comprising cathode 25 andaccelerating electrode 28, for the purpose of avoiding spurious efitectsattributable to secondary electron emission. Further, the particularconstruction of deflection-control systems 36, 37 and 43, 44 may bevaried; for example, one or more of the deflection electrodes may bereplaced by plural electrodes biased at different potentials, such ascathode potential and the DC. supply voltage of the associated apparatuswith which the tube is employed. Preferably, however, deflectionelectrodes 43 and 44 in the left-hand section of the tube areconstructed as simple parallel rods or wires to minimize theintercepting area presented to stray electrons. Still further, either orboth of the sheetlike electron beams may be split into two or more beamssubjected to a common transverse deflection field or to synchronousdeflection fields without departing from th spirit of the invention.

The electrode system is mounted within a suitable envelope (not shown)which may then be evacuated and the art. Theentir e structure mayconveniently be 1T1:

cluded in a miniature glass envelope, a number of electrode connectionsbeing made internally of the envelope in a manner to be made apparent,for the purpose of v minimizing the number of external circuitconnections.

In operation, deflection plates 36 and 37 are biased to direct theelectron beam in the right-hand section of the tube to anelectron-impervious portion of target electrode 29, for example, to asolid portion of electrode 29 on the side of aperture 30 nearerdeflection plate 36. When an input signal of positive polarity isapplied to deflection plate 37, or alternatively when an input signal ofnegative polarity is applied to deflection plate 36, the beam isdeflected at least partially into slots 34) and 31 whenever the inputsignal exceeds a predetermined amplitude level. During such intervalscurrent is permitted to flow in the output circuits associated withelectrodes 33, 34 and 35, provided these electrodes are maintained at aproper potential to receive electrons, while during other intervals nosuch current flow can occur. Moreover, when the input signal exceeds apredetermined higher amplitude, the beam is deflected beyond slot 30 ofintercepting electrode 29, and current flow to output electrodes 33 and34 is again interrupted. At still greater input-signal amplitudes, thecurrent flowing to output electrode 35 is first diminished as the beamis deflected into extension 32 of slot 31 and then extinguished as thebeam sweeps beyond extension 32.

The transfer characteristics of the input deflectioncontrol system 36,37 with respect to the output system comprising electrodes 33 and 34-and with respect to output electrodes 35 are represented by curves 51and.

52 respectively of Figure 4. Curve 51 represents the total current (i -Hflowing to controllector electrodes 33 and 34 as a function of the inputvoltage e applied to deflection-control system 36, 37. Curve 52 showsthe current i to output electrode 35 as a function of the input voltagee The magnitudes and shapes of curves 51 and 52 are determined by thegeometry of slots 30 and 31; the particular operating characteristicsillustrated in Figure 4 are those obtained for a specific embodiment andare not intended to be construed as representing required relative orabsolute magnitudes or shapes. 7

Receptor electrodes 33 and 34, which each comprise electricallyconnected control and collector portions and are therefore termedcontrollector electrodes, are disposed in effectively symmetricalrelation with respect to the tube axis 42 passing through the center ofslot 30 and, in operation, are preferably biased to equal positiveunidirectional operating potentials. The collector portions conjointlydefine a collector system for collectively receiving substantially allelectrons projected through slot 30, and the control portions serve as adeflection-control system responsive to applied signals for controllingthe "space current distribution between the collector portions.

The control characteristics of controllector electrodes 33 and 34 areshown qualitatively in Figure 5, in which curve 53 represents thecurrent i t0 electrode 33 and curve 54 the current i 34 to electrode 34as functions of the potential difference e -e between the twocontrollectorelectrodes. As described in Adler application Serial No.263,737, it has been found that the current distribution betweencontrollector electrodes 33 and 34 may be made substantially independentof the position at which the beam enters slot 30 of target electrode 29.This desirable condition may be obtained over a broad range of positivebias potentials for controllector electrodes 33 and 34, as for examplebetween one-fifth and one-third of the voltage applied to targetelectrode 29. 'When" so operated, target electrode 29 and controllectorelectrodes 33 and 34 form an electrostatic 'lens for focusing the beam,whenever it passes through slot 30, A

to. converge on the collector system at a location subgettered inaccordance with well known procedures in stantially independent of theinput signal applied between deflection-control electrodes 36 and 37.Thus, in practice, it has been found thatthe operating characteristicsof Figure remain substantially unchanged throughout a fairly large rangeof positive bias potentials for controllector electrodes 33 and34.Curves .53 and 54 intersect symmetrically, for an effectivelysymmetrical physical construction, and the current is divided equallybetween electrodes 33 and734 whentheir potentials are equal. electrodes33 and 34- are effectively trapped in-.,the enclosed region betweenthese electrodes;

The left-hand portion of the. structure of Figure 2 constitutes aconventional deflection-control electrodesystem. The electron beamprojected through focusing and.

accelerating electrodes 38 and 39 is. directed either to anode 4% or toanode 41 in accordance with the instantaneous potential differencebetween electrostatic-deflectionelectrodes .43 and .44. If a sinusoidalsignal wave is applied betweendeflection electrodes 43 and 44, the beamis caused cyclically to sweep back and forth transversely across axis 42and is thereby switched back and forth between anodes 4d and 41.Consequently, since full beam current is switched from one anode to theother in a relatively small fraction of a cycle, oppositely phasedsquare-wave output signals are produced in load circuits respectivelyassociated with anodes 40 and 41; in the preferred embodimentof theinvention, only one squarewave output signal is required, and eitheranode 4th or anode 41 is employed to develop the output signal while theother is directly connected to accelerating electrode 39.- It ispreferredthat anode 40 be employed as the output anode in order to avoiddifliculties arising from secondary electron emission.

Electrondischarge device 23 or the receiver of Figure 1 is constructedin the manner shown and described in connection with Figures 2-5.Composite Video signals from first video amplifier 16 are supplied todeflection plate 37, hereinafter termed the active deflector, in theright hand section of device 23 by means of a voltagedivider networkcomprising resistors 6d and 61,, active defiector 37 being connected tothe junction between resisters 65 and 61. A condenser 62 is connected inparallel with resistor 60. Cathode ,25 of device 23 is connected toground. Accelerating electrodes 28 and 39, target electrode 2,'andsecond anode 41 are connected together (preferably internally oftheenvelope) and to a suitable source of positive unidirectionaloperating potential conventionally designated B+. Deflection plate 36,hereinafter termed the companion deflector, is connected to a tap on avoltage divider comprising resistors 63. and 65 connected between 3+ andground.

Synchronizing system 20 also comprises a line-frequency sweep system 67,which may include a discharge tube and a power output stage, forimpressing suitable deflection currents on line-frequency deflectioncoil 21 associated withimage-reproducing device 15. Controllectorelectrodes 33 and 34 of device 23 are respectively coupled to oppositeterminals of a coil 68, having a center tap 59 which isreturned toground through a resistor 70, by means of anti-hunt networks comprisingshunt-connected resistor-condenser combinations 71 and 72, andcondensers '73 and 74. A tuning condenser 75 is connected in parallelwith coil 63, and a conductive load impedance, such as a pair of equalresistors 76 and 77, is connected between electrodes 33 and 34, thejunction 78 between resistors 76' and 77 being connected to a suitablepositive bias potential source, as by connection to a tap 79 of avoltage divider 89 connected between B+ and ground. Coil 68 is energizedby a feedback coil 81 which is preferably connected in series betweenline-frequency deflection coil 21 and ground, as indicated by theterminal designationsX-X. Center tap 69 of coil 68 is also coupledthrough anintegrator 82 to a field-frequency scanning system 83 whichprovides suitable deflection currents. to. field frequency deflectioncoil 22 associated with image-reproducing device 15.

Secondary electrons originating at: controllector Y Controllectorelectrodes 33 and 34 are directly connected to electrostatic-deflectionelectrodes 43 and 44 respectively inthe left-hand section of device.23,and anode 4l -is connected to 13+ through a load resistor 84 and toline-frequency sweep system 67 through a dif-' ferentiatingnetworkcomprising a series condenser 85 and a shunt resistor 86.

Plate electrode 35 is connected to B+- through a resistor 37 and arheostat 33 and is also returned through series-connected resistors 89and 90 to focusing electrode 8 which, in accordance with one feature ofthe invention, constitutes a suitable source of'negative unidirectionaloperating potential in a manner to be hereinafter described; inoperation, focusing electrode 38 may supply to resistor 99 a directvoltage of about 50 volts negative with respect to cathode 25. Anintegrating condenser 91 is connected between plate'electrode 35 andground. The junction 92 between resistors 89 and 90 is connected to theautomatic gain control (AGC) lead 93 and is shunted by a filtercondenser 94,-and AGC lead 93 is connected to one or more of thereceiving circuits comprising radio-frequency amplifier 1'1,oscillator-converter l2, and intermediate-frequency amplifier 13.

If desired, either the tube structure or the external circuitry, orboth, may be modified to compensatefor decentering of the reproducedimage-attributable to the unique phase relations between the incomingsynchroniz-- ing pulses and the scanning signals encountered-in thepresent system, as described and-claimed in the copcnding application ofRobertAdler, Serial No. 272,200, filed February 18, 1952, now Patent No.2,781,468, issued February 12, 1957, for- Television Receiver, andassigned to the present assignee. Moreover, a weak signal compensationmay beprovided in the manner describedand claimed in the copendingapplication-of Robert Adler, Serial No. 304,698, filed August 16, 1952,for Telc vision Receiver, also assigned to the present assignee.

The system thus far describedeorresponds'in its fundamental aspects tothose disclosed in one or more of'the-H above-identified copendingapplications. In accordance with the present invention, however, thesystem is moth-- lied to cut off the beam in the power section ofelectrondischarge device 23 during a major portion of each scanningcycle. To this end, a phase-shifting network com-- prising a condenser95 and a resistor 96 is connectedin parallel with parallel-resonantcircuit 68, 75, and the junction 97 between condenser 95 and resistor 96is coupled to focusing electrode 33in the power section of device 23 bymeans of'a coupling condenser 93, focus ing electrode 33 being-returnedto ground throughe high resistance 99.- Focusing e1ectrode'38 is alsoconnected to AGC lead 93 through resistor 30.

The construction and operation of synchronizing and-- automatic gaincontrol system 25 are generally similar to those disclosed and claimedin certain of the aboveidentifiedcopending applications, and theoperation willfirst be describedin its more generalaspects without regard to the beam-gating action of the present invention.Positive-polarity composite video signals, including the direct-voltagecomponents, from the output circuit 0ffirst video amplifier 16 areapplied to active deflector 37 by means-of the voltage divider networkcomprising resistors wand 61 and condenser 62. Deflectors 36 and 37 areso biased that the beam projected through aperture 27 of acceleratingelectrode 28 is normally-directed to anelectron-impervious portion oftarget eleca flected entirely into aperture 30 and partially into aper-9 tu're 31 of intercepting anode 29 in response to thesynchronizing-signal components of the applied composite video signals;the beam is entirely intercepted by target electrode .29 and/ordeflection plate 36 during video-signal intervals, As a consequence,beam current is only permitted to flow to electrodes 33, 34 and 35during synchronizing-pulse intervals.

The left-hand section of device 23 serves as a linefrequency oscillatorin the line-frequency scanning system. Oppositely phased sinusoidalsignals are applied to defledtion electrodes 43 and 44 by means of coil68 and condenser 75 which are tuned to the line-scanning frequency tooperate as an oscillatory circuit or filter excited by means of coil 81inserted in series with the line-frequency deflection coil 21.Consequently, the beam in the left-hand section of device 23 is causedto sweep back and forth between anodes 40 and 41, so that arectangular-wave output voltage is developed across resistor 84. Thisoutput voltage is difierentiated by means of condenser 85 and resistor86, and the resulting positivepolarity or negative-polarity pulses areemployed to trigger line-frequency sweep system 67, depending on theconstruction of that sweep system.

At the same time, the same oppositely phased sinusoidal voltage wavesapplied to deflection electrodes 43- and 44 are impressed oncontrollector electrodes 33 and 34, respectively in the right-handsection of device 23. As previously explained, current flow tocontrollector electrodes 33 and 34 is restricted to synchronizing-pulseintervals by virtue of the geometry of target electrode 29. The currentdistribution between electrodes 33 and 34 is dependent upon theinstantaneous potential difference between these electrodes during thesynchronizingpulse intervals.

. The oppositely phased sinusoidal signals developed at the terminals ofcoil 68- by excitation of tuned circuit 68, 75 in response to the sweepcurrent through coil 81 serve as comparison signals in a balancedphase-detector. If the comparison signals are properly phased withrespect to the incoming line-frequency synchronizingsignal pulses, theinstantaneous potentials of controllector electrodes 33 and 34 are equalat the time of arrival of each synchronizing pulse, and the spacecurrent passing through aperture is equally divided between electrodes33 and 34, with the result that no unidirectional control potentialdifference is developed between the controllector electrodes. parisonsignals and the incoming line-frequency synchronizing-signal pulses arenot in proper phase synchronism, the instantaneous potentials of the twocontrollector electrodes 33 and 34 at the time of arrival of eachlinefrequency synchronizing-signal pulse are different, so that the beamcurrents collected by electrodes 33 and 34 are unequal and a balancedunidirectional control voltage is developed between the controllectorelectrodes. Since controllector electrodes 33 and 34 are directlyconnected to deflection electrodes 43 and 44 respectively in theleft-hand section of device 23, the beam in the lefthand section isaccelerated or retarded in its progress from anode to anode 41 and backin response to the unidirectional control voltage. As a result, :thepositive and negative half-cycles of the output voltage wave developedacross resistor 84 are altered in time duration with respect to eachother in accordance with the unidirectional control potential diiferencebetween electrodes 33 and 34. The quasi-square wave thus developed isdiiferentiated to provide triggering pulses for line-frequency sweepsystem 67. Since the triggering pulses arev derived by differentiatingthe leading or trailing edges of the output quasi-square wave, and sincethe timing of these leading and trailing edges is varied in accordancewith the developed AFC potential, phase synchronism of theline-frequency sweep system with the incoming line-synchronizing pulsesis assured.

In order to obtain the desired automatic-frequency- On the other hand,if the comcontrol action, it is essential that a condition in which thecomparison signals lag the incoming synchronizingsignal pulses result inan increase in the frequency of the local oscillator comprising theleft-hand section of device 23, line-frequency sweep system 67, andfeedback circuit 81, 68. This operation is insured by the common directconnections for both the sinusoidal comparison signals and theundirectional AFC potential from controllector electrodes 33 and 34 todeflection electrodes 43 and 44 respectively. It is possible, for agiven construction of sweep system 67, that the system may fail tooscillate altogether due to incorrect phasing of the comparison signalsand the triggering pulses for the line-frequency sweep system; thiscondition may be corrected by merely reversing the terminal connectionsof feedback coil 81 or of coil 68. Proper pull-in action isautomatically insured for any condition for which oscillation isobtained.

To obtain field-frequency synchronization, the output currents tocontrollector electrodes 33 and 34 are effectivel-y combined by means ofresistor connected in the common ground return for controllectorelectrodes 33 and 34. The combined output appearing across resistor 70is integrated by integrator 82 to provide a control signal forfield-frequency scanning system 83. The beam current through aperture30, representing the clipped syncpulses, is first used in its entiretyto provide a balanced line-frequency control potential, and then againin its entirety to synchronize the field scansion. The use of an outputload impedance connected in a com anon return circuit for thephase-detector electrodes for deriving field-frequency driving pulses isspecifically described and claimed in the copending application ofRobert'Adler, Serial No. 260,221, filed December 6, 1951, now Patent No.2,740,002, issued March 27, 1956, entitled Balanced Sync Separator andPhase Comparator System and assigned to the present assignee. It is alsopossible to employ a separate plate electrode for the sole purpose ofdeveloping field-frequency synchronizingsignal pulses for application tothe field-frequency scanning system, as described in Spracklenapplication Serial No. 246,768.

Plate electrode 35 develops a unidirectional control potentialindicative of the peak amplitude of the composite video signals forapplication to the receiving circuits preceding the video detector toeffect automatic gain control of the receiver. Plate electrode 35 isconditioned to receive substantially all beam current directed t heretobyviltue of its connection to 13+ through resistor 87 and rheostat 88.During video-signal intervals, however, the input signal amplitude atactive deflector 37 is not suflicient to cause deflection of spaceelectrons through slot 31, with the result that space current is onlypermitted to flow to plate electrode 35 during synchronizing-pulseintervals. Noise pulses occurring during either synchronizing-pulseintervals or video-signal intervals are generally of much greateramplitude than the peak amplitude of the synchronizing pulses and thuscause deflection of the beam beyond slot 31. This results in anaperture-gating characteristic, as distinguished from the now-familiartime-gated automatic gain control system, with theautomatic-gain-control potential being dependent substantially only onthe peak amplitude of the synchronizing pulses. Series-connectedresistors 87, 88,

89 and 9t) constitute a voltage divider between B-land focusingelectrode 38 and are so proportioned that, in the absence of spacecurrent to plate electrode 35, the potential of AGClead 93 is at or nearground, depending upon the required bias voltage for receiving circuits11, 12 and 13. The potential of junction 92 varies in accordance withthe space current to plate electrode 35 and is then filtered bycondenser 94 and applied to AGC lead 93 to eifect automatic gain controlof'the receiver. In other words, plate electrode 35 isv coupled to anintermediate point on the voltage divider comprising resisll tors 87,38, 89 and 99 to cause the potential at another intermediate point 92 tovary in response to variations inthe' peak-amplitude of thesynchronizing pulses applied to active deflector 37 from first videoamplifier 16.

Certain important advantages of the system may best be understood from aconsideration of Figures 2-4. Since aperture 3% in intercepting anode 2?has definite fixed boundaries, it is apparent that deflect-ion of thebeam'beyond aperture 36 results in interception thereof by ianode 29.Consequently, extraneous noisepulses, which'are generally of much largeramplitude any desired component of the composite video signals, are nottranslated to controllector electrodes 33 and 34, and loss ofsynchronization due to extraneous impulse noise is substantiallyprecluded. This operation is apparent from opera-ting characteristic 51of Figure 4. When composite video signals comprising synchronizing-pulsecomponents 160 and video-signal components Mil are impressed on activedeflector 37, extraneous noise pulses 102, N3 which are of greater peakamplitude than the synchronizing-pulse components by an amount exceedingthe voltage represented by the spacing between vertical lines 1694 andM5, result in deflection of the beam beyond aperture 3t consequently,these noise pulses are not translated to the output oircuits associatedwith controllector electrodes 33 and 34, and substantial noise immunityis achieved. Aperture 3% is preferably of constant length in a directionparallel to cathode 25, in order to provide output current pulses ofconstant amplitude for application to scanning system 53 and to insureproper AFC action in spite of such rapid fluctuations in the amplitudeof the synchronizing pulses as are occasionally encountered.

The operation of the automatic gain control system may perhaps best beunderstood by a consideration of operating characteristic '52 of Figure4. Space electrons are permitted to pass to plate electrode 35 only whenthe electron beam is laterally deflected at least partially intoaperture 31. in an equilibrium condition, the deflection-control systemis so biased that the peaks of the synchronizing-signal pulses areimpressed on the rising portion of characteristic 52, as indicated byvertical line 1%. When the signal amplitude increases, the peaks of thesynchronizing pulses 1% instantaneously extend further to the right, andthe space current to plate electrode 35 is increased. This results in anincrease in the negative unidirectional control potential applied to thereceiving circuits 11, 12 and 13, thus reducing the gain of thesecircuits and thereby restoring the amplitude of the input signal appliedto active deflector 37 to the equilibrium value indicated in thedrawing. On the other hand, if the signal amplitude instantaneouslydecreases, the negative gain-control potential decreases and the gain ofthe receiving circuits is increased to restore equilibrium. swing thebeam beyond slot extension 32 are prevented from contributing materiallyto the automatic gain control potential by virtue of the finiteboundaries of aperlure 31. Noise pulses of lesser amplitude than pulse102,

such as pulse 103, contribute only very slightly to the automatic gaincontrol potential by virtue of the restricted access to plate electrode735 afforded by slot extension 32. Consequently, the aperture gatingcharacteristic 52 of the AGC system provides substantial noise immunitywhich in practice has been found favorably comparable with that obtainedby the use of conventional time-gated automatic gain control systems.Extension 32 of slot 31 is provided for the purpose-of avoidingparalysis of the AGC system, as described in application Serial No.242,509.

Since it is desirable for the synchronizing current pulses developedatcontrollector electrodes 33 and 34 to be of constant amplitude; it ispreferred that the peaks of the synchronizing-pulse components 109 beimpressed on characteristic. 51 at aconstan'ccurrent region of thatNoise pulses of sufiicient amplitude to characteristic; in other words,the synchronizing-pulse components of the applied composite videosignals should cause deflection of the upper portion of the beamentirely into aperture 30. At the same time, because of the automaticgain control action, the peaks of the synchronizingpulse components arenormally superimposed on a sloping portion of characteristic 52; inother Words, the synchronizing-pulse components of the applied compositevideo signals cause deflection of the lower portion of the beam onlypartially'into aperture 31. By disposing apertures 3% and 31 inoverlapping or staggered alignment in a direction parallel to cathode25, as illustrated in Figure 3, it is insured that whenever theautomatic gain control action establishes the equilibrium conditionillustrated by the graphical representation of Figure 4, synchronizingcurrent pulses of constant amplitude are developed at controllectorelectrodes 33 and 34; in other Words, the clipping level of thesynchronizing-signal separator is automatically adjusted in spite ofvarying signal strengths at the receiver input. The directvoltage-to-alternating voltage transmission ratio of the voltage-dividernetwork comprising resistors 60 and 61 and condenser 62 may be adjustedto a value of less than unity to preclude receiver paralysis undercertain abnormal operating conditions, in the manner described andclaimed in the copending application of John G. Spracklen, Serial No.259,063, filed November 30, 1951, now Patent No. 2,684,403, issued July20, l954,'for Television Receiver and assigned to the present asisgnee.

While the operation of the system is exceedingly stable and reliable, ascompared to presently known systems, certain unique problems have beenencountered owing to the specific construction'of the tube and itscircuit connections. Application of the comparison signals from tunedcircuit 68, 75 to the deflectors 43 and 44- in the power section of thetube results in a periodic lateral deflection of the beam in the powersection of the tube.

It has been found that deflectors 43 and 44, even when constructed assimple parallel rods or wires, may 'draw' beam current at the peaklateral excursions of the beam.-

By virtue of the direct connections between deflectors 43 and 4-4 andphase detectoranodes $3 and 34-- respectively, any beam current drawnbydeflectors 43 and 44: results in a drop in the average voltageof'phase detector anodes 33' and '34, an eflect which isindistinguishable from the flow of excessive beam current through syncclipping slot 36) in the control section of the tube and of theautomatic which may lead to instability or collapse frequency controlsystem.

In accordance with the present invention, this collapse parison signalapplied to deflectors 33 and 44, .so that no beam current may beintercepted by these deflectors.

At the same time, the gating of the beam in the power section has afurther salutary effect in reducing the amount of current drawn by thepower section of the tube.v

This aspect of the invention may perhaps be morereadily understood by.reference to the graphical representation of Figure 6 in which severalwaveforms are plotted as functions of time. Curve A represents thecomparison signal applied between deflectors 43 and 44 of the powersection and, for a condition of exact phase synchronism between theincoming line-synchronizing pulses and the comparison signal, iscentered about an axis 116 corres ondin to the intercepting edeofoutouta a l anode 40. I

Comparison signal Ais also applied across the phase- Speciflcally, agating' 13 shifting network comprising series-connected condenser 95 andresistor 96, and the voltage appearing across resistor 96, representedby curve B, is in substantial phase quadrature with comparison signal A,leading the latter by 90 electrical degrees. Gating signal ,3 is appliedto focusing electrode 38 in the power section of the tube by means ofcoupling condenser 98 and resistor 99 which serve as a self-biasinginput circuit to establish the gating signal B at an appropriate levelwith respect to the cutoff voltage, represented by dot-dash line 111, offocusing electrode 38L Application of gating signal B to focusingelectrode 38 permits the generation of an electron beam in the powersection only during intervals when the focusing electrode potentialexceeds its cutoff level 111, rep-- resented by the intervals betweenvertical dotted lines 112 and 113. If the horizontal dot-dash lines 114in curve A of Figure 6 represent the threshold potentials of deflectors43 and 44 beyond which they commence to draw beam current, it isapparent thatthe application of the gating signal B to focusingelectrode 38 prevents the interception of beam current by deflectors 43and 44 bycutting off the beam during those intervals when the comparisonsignal exceeds the threshold values 114.

The voltage developed at output anode 40 is represented by curve C ofFigure 6. When the beam in the power section is first turned on, as thegating signal B exceeds the cutoff level 111 of focusing electrode 38 atthe time represented by the vertical dash line 115, output anode 4tbegins to draw beam current. Consequently, the potential of output anode40 drops until the time repre sented by vertical dash line 116 when thepotentials of deflectors 43 and 44 are equal. At that instant, the beamsweeps beyond the intercepting edge of output anode 40 and is thereafterdirectedto collector anode 41. Consequently, the potential of outputanode 40 rises rapidly to its nominal or steady state value as the beamsweeps from anode 40 to anode 41. The voltage C developed by outputanode 40 and appearing across load resistor 84 is differentiated bymeans of condenser 85 and resistor 86 to provide a differentiated signalof the waveform indicated in curve D of Figure 6, and thepositive-polarity pulse components 117 of the differentiated outputsignal D are employed to trigger the discharge tube'of line-frequencysweep system 67. g

Any phase deviation of the comparison signal with respect to theincoming line-synchronizing pulses results in the generation of anautomatic-frequency-control voltage between phase detector anodes 33 and34, as explained above. This AFC voltage is applied to deflectors 43 and44 by virtue of the same direct connections through which the comparisonsignal is supplied. Superposition of the unidirectional AFC voltage onthe alternating comparison voltage results in an effective shift of itsAC axis with respect to the intercepting edge of output anode 40. InFigure 6, the conditions of maximum phase deviation in either directionfrom synchronism have ben indicated by showing an effective displacementof the intercepting edge of output anode/i0 by an I amount correspondingto the largest magnitude of the AFC voltage; however, it should beclearly understood that the position of the intercepting edge is a fixedelement of tube construction, and the efliective displacementillustrated in Figure 6 is shown only for the purpose of avoiding unduecomplication of the drawing. At a condition of maximum phase deviationin one direction, the crossover ofthe beam in the power section from theactive anode 40 to the collector anode 41 occurs at an instantrepresented by dot-dash line 118, earlier than the time of crossover 116when the system is operating in correct phase. On the other hand, undera condition of maximum phase deviation in the opposite direction, thebeam crossover occurs at a time 119 which is later than the normalcrossover time 116. As a' result, the trailing edge of the outputvoltage pulses of curve C is shifted accordingly, and the position ofthe trigger pulses 117 of the differentiated output voltage wave D isadvanced or delayed as indicated by the dashed lines 120 and 121 inaccordance with the magnitude and direction of unbalance of the AFCvoltage.

From the foregoing description, it is apparent that the waveform of thegating signal is not critical to the op eration of the presentinvention; in the embodiment of Figure 1, a sinusoidal gating signal inphase quadrature with the comparison signal is employed for thispurpose, but equivalent results may be obtained by employing pulse-typegating signals, derived either from the com parison signal or directlyfrom the sweep output, in the proper phase with respect to thealternating voltageapplied to the deflectors in the power section of thetube. Thus, for example, positive-polarity flyback pulses may be derivedfrom a tap on the primary winding or from a separate secondary windingof the line-frequency sweep transformer and applied, after integration,to'focusi-ng electrode 38 to provide the desired gating action.

In accordance with another feature of the invention, the focusingelectrode is also employed as a rectifying diode plate to produce aunidirectional negative bias potential which is superimposed on theautomatic-gaincontrol voltage to provide a modified AGC voltage forapplication to the receiving circuits. In order for the focusingelectrode to function in this manner, it is essential that at least aportion of the focusing electrode be directly exposed to the emissivesurface of the cathode; for this reason, it is preferred to employ afocusing electrode which is electron-impervious except for a slotcentered with respect to and narrower than the emissive surface of thecathode. Application of the gating signal to the focusing electrodethrough coupling condenser 98 produces a charge across the couplingcondenser during the conductive portions of each operating cycle, andthis negative voltage is smoothed by resistor and condenser 94 andcombined with the AGC voltage appearing at AGC plate 35 to provide amodified AGC signal having the proper average magnitude for applicationto the control grids of the receiving stages. The use of the focusingelectrode as a diode plate, in addition to its functions as a focusingelectrode and as a beam-gating electrode, results in the elimination ofa battery or a separate diode for the development of the requirednegative bias potential for the AGC system.

While the invention is of particular utility in connec tion with asynchronizing system employing a special purpose electron-dischargedevice of the type described, entirely equivalent performance may beobtained with separate electron-discharge devices corresponding to thecontrol section and the power section of device 23 respectively.Moreover, the invention may-also be employed to advantage in receiversprovided with other types of automatic frequency control and automaticgain control systems operating in conjunction with a beam deflectionpower tube constructed in the manner'of the left-hand section of thedevice of Figure 2. For example, the automatic frequency control systemmay comprise a completely conventional double-diode balanced phasedetector, and the automatic gain control system may be of a conventionaltype employing an amplitude-delay biased diode or triode rectifier whichmay be time gated if desired. Moreover, the negative bias voltagedeveloped at the gating electrode may be applied to any direct-voltageutilization circuit requiring a negative energizing potential. Finally,it is not essential that the gating signal be applied to afocusing'electrode; any electrode exerting an intensity-controlinfluence on the electron beam of the power tube, either in the form ofa slotted plate or a mesh grid, may be employed for this purpose,although it is preferred that the gating electrode'be disposed closelyadjacent the cathode emissive surface in embodiments in which it isdesired to employ the gating electrode in the generation of a negativebias potential.

'While a particular embodiment of the present invention has been shownand described, it is apparent that" 15 various changes and modificationsmay be made, and it is therefore contemplated in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:

1. In a television receiver: an image-reproducing device; a scanningsystem associated with said imagereproducing device for controlling thescansion thereof; a source of composite video signals; means coupled tosaid composite video signal source andto said scanning system foreffecting a phase comparison of the synchronizing components of saidwmposite video signals with a comparison signal generated by saidscanning system to develop a unidirectional automatic-frequency-controlvoltage; an electron discharge device comprising an electron gunincluding a cathode for generating an electron beam, asintensity-control electrode for intensity-modulating said beam, and anaccelerating electrode for projecting said beam along a beam path, acontrol system for controlling the passage of said beam along said path,and an output electrode system for. intercepting said beam; means forapplying said comparison signal and said automatic-frequency-controlvoltage to said control system; means for applying a gating signal tosaid intensity-r control electrode to permit the passage of spaceelectrons to said output electrode system during only a minor portion ofeach scanning cycle; and means coupling said output electrode system tosaid scanning system to synchronize said scanning system with saidsynchronizing components of saidrcomposite video signals.

2. In a television receiver: an image-reproducing device; a scanningsystem associated with said image-reproducing device for controlling thescansion thereof; a source of composite video signals; means including abalanced phase detector, having a pair of output electrodes, coupled tosaid composite video signal source and to said scanning system foreffecting a phase comparison of the synchronizing components of saidcomposite video signals with a comparison signal generated by saidscanning system to develop a balanced unidirectionalautomatic-frequency-control voltage between said output electrodes; abeam deflection tube comprising an electron gun including a cathode forgenerating an electron beam, an intensity-control electrode forintensity-modulating said beam, and an accelerating electrode forprojecting said beam along a beam path, a control system including apair of deflection-control electrodes for controlling the passage ofsaid beam along said path, and an output electrode system forintercepting said beam; means, including means individually directcoupling said output electrodes to said deflection-control electrodes,for applying said comparison signal and said automatic-frequency-controlvoltage to said control system; means coupled to said scanning systemfor applying a gating signal to said intensity-control electrode topermit the passage of space electrons to said output electrode systemduring only a minor portion of each scanning cycle; and means couplingsaid output electrode system to said scanning system to synchronize saidscanning system with said synchronizing components of said compositevideo signals.

3. In a television receiver: an image-reproducing device; a scanningsystem associated with said image-reproducing device fior controllingthe scansion thereof; a source of composite video signals; means coupledto said composite video signal source and to said scanning system foreifecting a phase-comparison of the synchronizing components of saidcomposite video signals with a comparison signal generated by saidscanning system to develop a unidirectional automatic-frequency-controlvoltage; a beam deflection tube comprising an electron gun including acathode for generating an electron beam, an intensity-control electrodefor intensity-modulating said beam, and an accelerating electrode-forprojecting said beam along a beam path, a deflection-control system forcontrolling the passage of said beam along said path, and

16 an output electrode system for intercepting said beam; means forapplying said comparison signal and said automatic-firequency-controlvoltage to said deflection-control system; means including aphase-shifting network coupled to said scanning system for applying agating signal in phase quadrature with said comparison signal to saidintensity-control electrode to permit the passage of space electrons tosaid output electrode system during only a minor portion of eachscanning cycle; and means coupling said output electrode system to saidscanning system to synchronize said scanning system with saidsynchronizing components of said composite video signals.

4. In a television receiver: an image-reproducing device; aline-frequency scanning system associated with said image-reproducingdevice for controlling the linefrequency scansion thereof; a source ofcomposite video signals; a parallel resonant circuit tuned to saidline-frequency and coupled to said scanning system for developing acomparison signal having a predetermined fixed phase relation with saidline-frequency scansion; means including a balanced phase detectorhaving an input circuit coupled to said composite video signal sourceand having a pair of output electrodes coupled to said parallel resonantcircuit for effecting a phase-comparison of the synchronizing componentsof said composite video signals with said comparison signal to develop abalanced unidirectional automatic-frequency-control voltage between saidoutput electrodes; a beam deflection tube comprising an electron gunincluding a cathode, an intensity-control electrode, and an acceleratingelectrode, a deflection-control system including a pair ofelectrostatic-deflection electrodes, and an output electrode systemincluding an output anode; means individually direct coupling saidoutput electrodes to said electrostaticdeflection electrodes to applysaid comparison signal and said automatic-frequency-control voltage tosaid deflection-control system; a phase-shifting network coupled to saidparallel resonant circuit for developing a gating signal in substantialphase quadrature with said comparison signal; means for applying saidgating signal to said intensity-control electrode to prevent the passageof space electrons to said output electrode system except during a minorportion of each line-frequency scanning cycle; and means coupling saidoutput anode to said scanning system to synchronize said scanning systemwith said synchronizing components of said composite video signals.

5. In a television receiver: an image-reproducing device; aline-frequency scanning system associated with said image-reproducingdevice for controlling the linefrequency scansion thereof; a source ofcomposite video signals; a parallel resonant circuit tuned to said linefrequency and coupled to said scanning system for developing acomparison signal having a predetermined fixed phase relation with saidline-frequency scansion; means including a balanced phase detectorhaving an input circuit coupled to said composite video signal sourceand having a pair of output electrodes coupled to said parallel resonantcircuit for eifecting a phase comparison of the synchronizing componentsof said composite video signals with said comparison signal to develop abalanced unidirectional automatic-frequency-control voltage between saidoutput electrodes; a beam deflection tube comprising an electron gunincluding a cathode, an intensity-control electrode, and an acceleratingelectrode, a deflection-control system including a pair ofelectrostatic-deflection electrodes, and an output electrode systemincluding an output anode; means individually direct coupling saidoutput electrodes to said electrostatic-deflection electrodes to applysaid comparison signal and said automatic-frequency-control voltage tosaid deflection-control system; a phase-shifting network including acondenser and a resistor seriesconnected in parallel with said parallelresonant circuit for developing a gating signal in substantial phasequadrature with said comparison signal; means including a condenser.coupled from the junction of said first-mentioned condenser and saidresistor to said intensity-control electrode for applying said gatingsignal to said intensity-control electrode to prevent the passage ofspace electrons to said output electrode system except during a minorportion of each line-frequency scanning cycle; and means coupling saidoutput anode to said scanning system to synchronize said scanning systemwith said synchronizing components of said composite video signals.

6. \In a television receiver: an image-reproducing device; aline-frequency scanning system associated with said image-reproducingdevice for controlling the linefrequency scansion thereof; a source ofcomposite video signals; a parallel resonant circuit tuned to said linefrequency and coupled to said scanning system for developing acomparison signal having a predetermined fixed phase relation with saidline-frequency scansion; means including a balanced phase detectorhaving an input circuit coupled to said composite video signal sourceand having a pair of output electrodes coupled to said parallel resonantcircuit for effecting a phase-comparison of the synchronizing componentsof said composite video signals with said comparison signal to develop abalanced unidirectional automatic-frequency-control voltage between saidoutput electrodes; a beam deflection tube comprising an electron gunincluding an elongated cathode, a slotted focusing electrode, and aslotted accelerating electrode, a deflection-control system including apair of electrostatic-deflection electrodes, and an output electrodesystem including an output anode; means individually coupling saidoutput electrodes to said electrostatic-deflection electrodes to applysaid comparison signal and said automatic-frequency-control voltage tosaid deflection-control system; a phase-shifting network coupled to saidparallel resonant circuit for developing a gating signal in substantialphase quadrature with said comparison signal; means for applying saidgating signal to said focusing electrode to prevent the passage of spaceelectrons to said output electrode system except during a minor portionof each line-frequency scanning cycle; and means coupling said outputanode to said scanning system to synchronize said scanning system Withsaid synchronizing components of said composite video signals.

7. In a television receiver: an image-reproducing device; a scanningsystem associated with said image-reproducing device for controlling thescansion thereof; a source of composite video signals; means coupled tosaid composite video signal source and to said scanning system foreffecting a phase-comparison of the synchronizing components of saidcomposite video signals with a comparison signal generated by saidscanning system to develop -a unidirectional automatic-frequency-controlvoltage; means coupled to said composite video signal source forgenenating a unidirectional automatic-gain-control voltage indicative ofthe peak amplitude of said synchronizing components; a beam deflectiontube comprising an electron gun including a cathode, an intensitycontrolelectrode, and an accelerating electrode, a deflection-control system,and an output electrode system; means for applying said comparisonsignal and said automatic-frequency-control voltage to saiddeflection-control system; means coupled to said scanning system forapplying a gating signal to said intensity-control electrode to permitthe passage of space electrons to said output electrode system duringonly a minor portion of each scanning cycle; means coupling said outputelectrode system to said scanning system to synchronize said scanningsystem with said synchronizing components of said composite videosignals; means coupled to said intensity-control electrode fordeveloping a unidirectional negative bias voltage; means for combiningsaid bias voltage with said automatic-gain-control voltage to provide amodified automatic-gain-control voltage; and means for utilizing saidmodified automatic-gain-control voltage to control an operatingcharacteristic of said receiver.

8. In a television receiver; image-reproducing device; a scanning systemassociated with said image-reproducing device for controlling thescansion thereof; a source of composite video signals; means coupled tosaid composite video signal source and to said scanning system foreffecting a phase-comparison of the synchronizing components of saidcomposite video signals with a comparison signal generated by saidscanning system to develop a unidirectional automatic-frequency-controlvoltage; means coupled to said composite video signal source forgenerating a unidirectional automatic-gain-control voltage indicative ofthe peak amplitude of said synchronizing components; a beam deflectiontube comprising an electron gun including a cathode having an elongatedemissive surface, a focusing electrode adjacent said cathode andprovided with a slot of smaller Width than said emissive surface, and anaccelerating electrode, a deflection-control system, and an outputelectrode system; means for applying said comparison signal and saidautomatic-frequency-control voltage to said deflection-control system;means coupled to said scanning system for applying a gating signal tosaid focusing electrode to permit the passage of space electrons to saidoutput electrode system during only a minor portion of each scanningcycle; means coupling said output electrode system to said scanningsystem to synchronize said scanning system with said synchronizingcomponents of said composite video signals; means coupled to saidfocusing electrode for developing a unidirectional negative biasvoltage; means for combining said bias voltage with saidantomatic-gain-control voltage to provide a modifiedautomatic-gain-control volt-age; and means for utilizing said modified'automatic-gain-control voltage to control an operating charcteristic ofsaid receiver.

9. In a television receiver: an image-reproducing device; a scanningsystem associated with said image-reproducing device for controlling thescansion thereof; a source of composite video signals; means coupled tosaid composite video signal source and to said scanning system foreffecting a phase-comparison of the synchronizing components of saidcomposite video signals with a comparison signal generated by saidscanning system to develop a unidirectional automatic-frcquency-controlvoltage; means coupled to said composite video signal source forgenerating a unidirectional automatic-gain-control voltage indicative ofthe peak amplitude of said synchronizing components; a beam deflectiontube comprising an electron gun including a cathode, an intensitycontrolelectrode, and an accelerating electrode, a deflection-control system,and an output electrode system; means for applying said comparisonsignal and said an tomatic-frequency-control voltage to saiddeflection-control system; means coupled to said scanning system forapplying a gating signal to said intensity-control electrode to permitthe passage of space electrons to said output electrode system duringonly a minor portion of each scanning cycle; means coupling said outputelectrode system to said scanning system to synchronize said scanningsystem with said synchronizing components of said composite videosignals; means including a condenser coupled to said intensity-controlelectrode for developing a unidirectional negative bias voltage; meansincluding a resistor coupled between said intensity-control electrodeand said automatic-gain-control voltage-generating means for combiningsaid bias voltage with said automatic-gaincontrol voltage to provide amodified automatic-gaincontrol voltage; and means for utilizing saidmodified automatic-gain-control voltage to control an operatingcharacteristic of said receiver.

References Cited in the file of this patent UNITED STATES PATENTSRoschke Oct. 20, 1953

